#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>
#include "gd.h"
#include "gdhelpers.h"

/* Code drawn from ppmtogif.c, from the pbmplus package
**
** Based on GIFENCOD by David Rowley <mgardi@watdscu.waterloo.edu>. A
** Lempel-Zim compression based on "compress".
**
** Modified by Marcel Wijkstra <wijkstra@fwi.uva.nl>
**
** Copyright (C) 1989 by Jef Poskanzer.
**
** Permission to use, copy, modify, and distribute this software and its
** documentation for any purpose and without fee is hereby granted, provided
** that the above copyright notice appear in all copies and that both that
** copyright notice and this permission notice appear in supporting
** documentation.  This software is provided "as is" without express or
** implied warranty.
**
** The Graphics Interchange Format(c) is the Copyright property of
** CompuServe Incorporated.  GIF(sm) is a Service Mark property of
** CompuServe Incorporated.
*/

/* a code_int must be able to hold 2**GIFBITS values of type int, and also -1 */
typedef int code_int;

#ifdef SIGNED_COMPARE_SLOW
typedef unsigned long int count_int;
typedef unsigned short int count_short;
#else /* SIGNED_COMPARE_SLOW */
typedef long int count_int;
#endif /* SIGNED_COMPARE_SLOW */

/* 2.0.28: threadsafe */

#define maxbits GIFBITS

/* should NEVER generate this code */
#define maxmaxcode ((code_int)1 << GIFBITS)

#define HSIZE	5003	/* 80% occupancy */
#define hsize	HSIZE	/* Apparently invariant, left over from compress */

typedef struct {
	int Width, Height;
	int curx, cury;
	long CountDown;
	int Pass;
	int Interlace;
	int n_bits;
	code_int maxcode;
	count_int htab [HSIZE];
	unsigned short codetab [HSIZE];
	/* first unused entry */
	code_int free_ent;
	/* block compression parameters -- after all codes are used up,
	 * and compression rate changes, start over. */
	int clear_flg;
	int offset;
	long int in_count;
	/* # of codes output (for debugging) */
	long int out_count;
	int g_init_bits;
	gdIOCtx * g_outfile;
	int ClearCode;
	int EOFCode;
	unsigned long cur_accum;
	int cur_bits;
	int a_count;
	char accum[ 256 ];
} GifCtx;

static int gifPutWord(int w, gdIOCtx *out);
static int colorstobpp(int colors);
static void BumpPixel(GifCtx *ctx);
static int GIFNextPixel(gdImagePtr im, GifCtx *ctx);
static void GIFEncode(gdIOCtxPtr fp, int GWidth, int GHeight, int GInterlace, int Background, int Transparent, int BitsPerPixel, int *Red, int *Green, int *Blue, gdImagePtr im);
static void GIFAnimEncode(gdIOCtxPtr fp, int IWidth, int IHeight, int LeftOfs, int TopOfs, int GInterlace, int Transparent, int Delay, int Disposal, int BitsPerPixel, int *Red, int *Green, int *Blue, gdImagePtr im);
static void compress(int init_bits, gdIOCtx *outfile, gdImagePtr im, GifCtx *ctx);
static void output(code_int code, GifCtx *ctx);
static void cl_block(GifCtx *ctx);
static void cl_hash(register count_int chsize, GifCtx *ctx);
static void char_init(GifCtx *ctx);
static void char_out(int c, GifCtx *ctx);
static void flush_char(GifCtx *ctx);

BGD_DECLARE(void *) gdImageGifPtr(gdImagePtr im, int *size)
{
	void *rv;
	gdIOCtx *out = gdNewDynamicCtx(2048, NULL);
	if (out == NULL) return NULL;
	gdImageGifCtx(im, out);
	rv = gdDPExtractData(out, size);
	out->gd_free(out);
	return rv;
}

BGD_DECLARE(void) gdImageGif(gdImagePtr im, FILE *outFile)
{
	gdIOCtx *out = gdNewFileCtx(outFile);
	if (out == NULL) return;
	gdImageGifCtx(im, out);
	out->gd_free(out);
}

BGD_DECLARE(void) gdImageGifCtx(gdImagePtr im, gdIOCtxPtr out)
{
	gdImagePtr pim = 0, tim = im;
	int interlace, BitsPerPixel;
	interlace = im->interlace;

	if(im->trueColor) {
		/* Expensive, but the only way that produces an
		acceptable result: mix down to a palette
		based temporary image. */
		pim = gdImageCreatePaletteFromTrueColor(im, 1, 256);
		if(!pim) {
			return;
		}
		tim = pim;
	}

	BitsPerPixel = colorstobpp(tim->colorsTotal);

	/* All set, let's do it. */
	GIFEncode(
	    out, tim->sx, tim->sy, interlace, 0, tim->transparent, BitsPerPixel,
	    tim->red, tim->green, tim->blue, tim);

	if(pim) {
		/* Destroy palette based temporary image. */
		gdImageDestroy(	pim);
	}
}

BGD_DECLARE(void *) gdImageGifAnimBeginPtr(gdImagePtr im, int *size, int GlobalCM, int Loops)
{
	void *rv;
	gdIOCtx *out = gdNewDynamicCtx(2048, NULL);
	if (out == NULL) return NULL;
	gdImageGifAnimBeginCtx(im, out, GlobalCM, Loops);
	rv = gdDPExtractData(out, size);
	out->gd_free(out);
	return rv;
}

BGD_DECLARE(void) gdImageGifAnimBegin(gdImagePtr im, FILE *outFile, int GlobalCM, int Loops)
{
	gdIOCtx *out = gdNewFileCtx(outFile);
	if (out == NULL) return;
	gdImageGifAnimBeginCtx(im, out, GlobalCM, Loops);
	out->gd_free(out);
}

BGD_DECLARE(void) gdImageGifAnimBeginCtx(gdImagePtr im, gdIOCtxPtr out, int GlobalCM, int Loops)
{
	int B;
	int RWidth, RHeight;
	int Resolution;
	int ColorMapSize;
	int BitsPerPixel;
	int Background = 0;
	int i;

	/* Default is to use global color map */
	if (GlobalCM < 0) {
		GlobalCM = 1;
	}

	BitsPerPixel = colorstobpp(im->colorsTotal);
	ColorMapSize = 1 << BitsPerPixel;

	RWidth = im->sx;
	RHeight = im->sy;

	Resolution = BitsPerPixel;

	/* Write the Magic header */
	gdPutBuf("GIF89a", 6, out);

	/* Write out the screen width and height */
	gifPutWord(RWidth, out);
	gifPutWord(RHeight, out);

	/* Indicate that there is a global colour map */
	B = GlobalCM ? 0x80 : 0;

	/* OR in the resolution */
	B |= (Resolution - 1) << 4;

	/* OR in the Bits per Pixel */
	B |= (BitsPerPixel - 1);

	/* Write it out */
	gdPutC(B, out);

	/* Write out the Background colour */
	gdPutC(Background, out);

	/* Byte of 0's (future expansion) */
	gdPutC(0, out);

	/* Write out the Global Colour Map */
	if(GlobalCM) {
		for(i = 0; i < ColorMapSize; ++i) {
			gdPutC(im->red[i], out);
			gdPutC(im->green[i], out);
			gdPutC(im->blue[i], out);
		}
	}

	if(Loops >= 0) {
		gdPutBuf("!\377\13NETSCAPE2.0\3\1", 16, out);
		gifPutWord(Loops, out);
		gdPutC(0, out);
	}
}

BGD_DECLARE(void *) gdImageGifAnimAddPtr(gdImagePtr im, int *size, int LocalCM, int LeftOfs, int TopOfs, int Delay, int Disposal, gdImagePtr previm)
{
	void *rv;
	gdIOCtx *out = gdNewDynamicCtx(2048, NULL);
	if (out == NULL) return NULL;
	gdImageGifAnimAddCtx(im, out, LocalCM, LeftOfs, TopOfs, Delay, Disposal, previm);
	rv = gdDPExtractData(out, size);
	out->gd_free(out);
	return rv;
}

BGD_DECLARE(void) gdImageGifAnimAdd(gdImagePtr im, FILE *outFile, int LocalCM, int LeftOfs, int TopOfs, int Delay, int Disposal, gdImagePtr previm)
{
	gdIOCtx *out = gdNewFileCtx(outFile);
	if (out == NULL) return;
	gdImageGifAnimAddCtx(im, out, LocalCM, LeftOfs, TopOfs, Delay, Disposal, previm);
	out->gd_free(out);
}

static int comparewithmap(gdImagePtr im1, gdImagePtr im2, int c1, int c2, int *colorMap)
{
	if(!colorMap) {
		return c1 == c2;
	}

	if(-2 != colorMap[c1]) {
		return colorMap[c1] == c2;
	}

	return (colorMap[c1] = gdImageColorExactAlpha(im2, im1->red[c1], im1->green[c1], im1->blue[c1], im1->alpha[c1])) == c2;
}

BGD_DECLARE(void) gdImageGifAnimAddCtx(gdImagePtr im, gdIOCtxPtr out, int LocalCM, int LeftOfs, int TopOfs, int Delay, int Disposal, gdImagePtr previm)
{
	gdImagePtr pim = NULL, tim = im;
	int interlace, transparent, BitsPerPixel;
	interlace = im->interlace;
	transparent = im->transparent;

	/* Default is no local color map */
	if(LocalCM < 0) {
		LocalCM = 0;
	}

	if(im->trueColor) {
		/* Expensive, but the only way that produces an
			acceptable result: mix down to a palette
			based temporary image. */
		pim = gdImageCreatePaletteFromTrueColor(im, 1, 256);
		if (!pim) {
			return;
		}
		tim = pim;
	}

	if (previm) {
		/* create optimized animation.  Compare this image to
		   the previous image and crop the temporary copy of
		   current image to include only changed rectangular
		   area.  Also replace unchanged pixels inside this
		   area with transparent color.  Transparent color
		   needs to be already allocated!
		   Preconditions:
		   TopOfs, LeftOfs are assumed 0

		   Images should be of same size.  If not, a temporary
		   copy is made with the same size as previous image.

		*/
		gdImagePtr prev_pim = 0, prev_tim = previm;
		int x, y;
		int min_x = 0;
		int min_y = tim->sy;
		int max_x = 0;
		int max_y = 0;
		int colorMap[256];

		if (previm->trueColor) {
			prev_pim = gdImageCreatePaletteFromTrueColor(previm, 1, 256);
			if (!prev_pim) {
				goto fail_end;
			}
			prev_tim = prev_pim;
		}

		for (x = 0; x < 256; ++x) {
			colorMap[x] = -2;
		}

		/* First find bounding box of changed areas. */
		/* first find the top changed row */
		for (y = 0; y < tim->sy; ++y) {
			for (x = 0; x < tim->sx; ++x) {
				if (!comparewithmap(prev_tim, tim,
				                    prev_tim->pixels[y][x],
				                    tim->pixels[y][x],
				                    colorMap)) {
					min_y = max_y = y;
					min_x = max_x = x;
					goto break_top;
				}
			}
		}

break_top:
		if (tim->sy == min_y) {
			/* No changes in this frame!! Encode empty image. */
			transparent = 0;
			min_x = min_y = 1;
			max_x = max_y = 0;
		} else {
			/* Then the bottom row */
			for (y = tim->sy - 1; y > min_y; --y) {
				for (x = 0; x < tim->sx; ++x) {
					if (!comparewithmap
					        (prev_tim, tim,
					         prev_tim->pixels[y][x],
					         tim->pixels[y][x],
					         colorMap)) {
						max_y = y;
						if(x < min_x) {
							min_x = x;
						}
						if(x > max_x) {
							max_x = x;
						}
						goto break_bot;
					}
				}
			}

break_bot:
			/* left side */
			for (x = 0; x < min_x; ++x) {
				for (y = min_y; y <= max_y; ++y) {
					if (!comparewithmap
					        (prev_tim, tim,
					         prev_tim->pixels[y][x],
					         tim->pixels[y][x],
					         colorMap)) {
						min_x = x;
						goto break_left;
					}
				}
			}

break_left:
			/* right side */
			for (x = tim->sx - 1; x > max_x; --x) {
				for (y = min_y; y <= max_y; ++y) {
					if (!comparewithmap
					        (prev_tim, tim,
					         prev_tim->pixels[y][x],
					         tim->pixels[y][x],
					         colorMap)) {
						max_x = x;
						goto break_right;
					}
				}
			}

break_right:
			;
		}

		LeftOfs = min_x;
		TopOfs = min_y;
		Disposal = 1;

		/* Make a copy of the image with the new offsets.
		   But only if necessary. */
		if (min_x != 0 || max_x != tim->sx - 1
		        || min_y != 0 || max_y != tim->sy - 1
		        || transparent >= 0) {

			gdImagePtr pim2 = gdImageCreate(max_x-min_x + 1, max_y-min_y + 1);

			if (!pim2) {
				if (prev_pim) {
					gdImageDestroy(prev_pim);
				}
				goto fail_end;
			}

			gdImagePaletteCopy(pim2, LocalCM ? tim : prev_tim);
			gdImageCopy(pim2, tim, 0, 0, min_x, min_y,
			            max_x - min_x + 1, max_y - min_y + 1);

			if (pim) {
				gdImageDestroy(pim);
			}

			tim = pim = pim2;
		}

		/* now let's compare pixels for transparent
		   optimization.  But only if transparent is set. */
		if (transparent >= 0) {
			for(y = 0; y < tim->sy; ++y) {
				for (x = 0; x < tim->sx; ++x) {
					if(comparewithmap
					        (prev_tim, tim,
					         prev_tim->pixels[min_y + y][min_x + x],
					         tim->pixels[y][x], 0)) {
						gdImageSetPixel(tim, x, y, transparent);
						break;
					}
				}
			}
		}

		if(prev_pim) {
			gdImageDestroy(prev_pim);
		}
	}

	BitsPerPixel = colorstobpp(tim->colorsTotal);

	/* All set, let's do it. */
	GIFAnimEncode(
	    out, tim->sx, tim->sy, LeftOfs, TopOfs, interlace, transparent,
	    Delay, Disposal, BitsPerPixel,
	    LocalCM ? tim->red : 0, tim->green, tim->blue, tim);

fail_end:
	if(pim) {
		/* Destroy palette based temporary image. */
		gdImageDestroy(pim);
	}
}

BGD_DECLARE(void) gdImageGifAnimEnd(FILE *outFile)
{
#if 1
	putc(';', outFile);
#else
	gdIOCtx *out = gdNewFileCtx(outFile);
	if (out == NULL) return;
	gdImageGifAnimEndCtx(out);
	out->gd_free(out);
#endif
}

BGD_DECLARE(void *) gdImageGifAnimEndPtr(int *size)
{
	char *rv = (char *) gdMalloc(1);
	if(!rv) {
		return 0;
	}
	*rv = ';';
	*size = 1;
	return (void *)rv;
}

BGD_DECLARE(void) gdImageGifAnimEndCtx(gdIOCtx *out)
{
	/*
	 * Write the GIF file terminator
	 */
	gdPutC(';', out);
}

static int colorstobpp(int colors)
{
	int bpp = 0;

	if(colors <= 2)
		bpp = 1;
	else if(colors <= 4)
		bpp = 2;
	else if(colors <= 8)
		bpp = 3;
	else if(colors <= 16)
		bpp = 4;
	else if(colors <= 32)
		bpp = 5;
	else if(colors <= 64)
		bpp = 6;
	else if(colors <= 128)
		bpp = 7;
	else if(colors <= 256)
		bpp = 8;

	return bpp;
}

/*****************************************************************************
 *
 * GIFENCODE.C    - GIF Image compression interface
 *
 * GIFEncode( FName, GHeight, GWidth, GInterlace, Background, Transparent,
 *            BitsPerPixel, Red, Green, Blue, gdImagePtr )
 *
 *****************************************************************************/

#define TRUE 1
#define FALSE 0

/* Bump the 'curx' and 'cury' to point to the next pixel */
static void BumpPixel(GifCtx *ctx)
{
	/* Bump the current X position */
	++(ctx->curx);

	/* If we are at the end of a scan line, set curx back to the beginning
	 * If we are interlaced, bump the cury to the appropriate spot,
	 * otherwise, just increment it. */
	if(ctx->curx == ctx->Width) {
		ctx->curx = 0;

		if(!ctx->Interlace) {
			++(ctx->cury);
		} else {
			switch(ctx->Pass) {

			case 0:
				ctx->cury += 8;
				if(ctx->cury >= ctx->Height) {
					++(ctx->Pass);
					ctx->cury = 4;
				}
				break;

			case 1:
				ctx->cury += 8;
				if(ctx->cury >= ctx->Height) {
					++(ctx->Pass);
					ctx->cury = 2;
				}
				break;

			case 2:
				ctx->cury += 4;
				if(ctx->cury >= ctx->Height) {
					++(ctx->Pass);
					ctx->cury = 1;
				}
				break;

			case 3:
				ctx->cury += 2;
				break;
			}
		}
	}
}

/* Return the next pixel from the image */
static int GIFNextPixel(gdImagePtr im, GifCtx *ctx)
{
	int r;

	if(ctx->CountDown == 0) {
		return EOF;
	}

	--(ctx->CountDown);

	r = gdImageGetPixel(im, ctx->curx, ctx->cury);

	BumpPixel(ctx);

	return r;
}

/* public */

static void GIFEncode(gdIOCtxPtr fp, int GWidth, int GHeight, int GInterlace, int Background, int Transparent, int BitsPerPixel, int *Red, int *Green, int *Blue, gdImagePtr im)
{
	int B;
	int RWidth, RHeight;
	int LeftOfs, TopOfs;
	int Resolution;
	int ColorMapSize;
	int InitCodeSize;
	int i;
	GifCtx ctx;

	memset(&ctx, 0, sizeof(ctx));

	ctx.Interlace = GInterlace;
	ctx.in_count = 1;

	ColorMapSize = 1 << BitsPerPixel;

	RWidth = ctx.Width = GWidth;
	RHeight = ctx.Height = GHeight;
	LeftOfs = TopOfs = 0;

	Resolution = BitsPerPixel;

	/* Calculate number of bits we are expecting */
	ctx.CountDown = (long)ctx.Width * (long)ctx.Height;

	/* Indicate which pass we are on (if interlace) */
	ctx.Pass = 0;

	/* The initial code size */
	if(BitsPerPixel <= 1) {
		InitCodeSize = 2;
	} else {
		InitCodeSize = BitsPerPixel;
	}

	/* Set up the current x and y position */
	ctx.curx = ctx.cury = 0;

	/* Write the Magic header */
	gdPutBuf(Transparent < 0 ? "GIF87a" : "GIF89a", 6, fp);

	/* Write out the screen width and height */
	gifPutWord(RWidth, fp);
	gifPutWord(RHeight, fp);

	/* Indicate that there is a global colour map */
	/* Yes, there is a color map */
	B = 0x80;

	/* OR in the resolution */
	B |= (Resolution - 1) << 4;

	/* OR in the Bits per Pixel */
	B |= (BitsPerPixel - 1);

	/* Write it out */
	gdPutC(B, fp);

	/* Write out the Background colour */
	gdPutC(Background, fp);

	/* Byte of 0's (future expansion) */
	gdPutC(0, fp);

	/* Write out the Global Colour Map */
	for(i = 0; i < ColorMapSize; ++i) {
		gdPutC(Red[i], fp);
		gdPutC(Green[i], fp);
		gdPutC(Blue[i], fp);
	}

	/* Write out extension for transparent colour index, if necessary. */
	if(Transparent >= 0) {
		gdPutC('!', fp);
		gdPutC(0xf9, fp);
		gdPutC(4, fp);
		gdPutC(1, fp);
		gdPutC(0, fp);
		gdPutC(0, fp);
		gdPutC((unsigned char) Transparent, fp);
		gdPutC(0, fp);
	}

	/* Write an Image separator */
	gdPutC(',', fp);

	/* Write the Image header */
	gifPutWord(LeftOfs, fp);
	gifPutWord(TopOfs, fp);
	gifPutWord(ctx.Width, fp);
	gifPutWord(ctx.Height, fp);

	/* Write out whether or not the image is interlaced */
	if(ctx.Interlace) {
		gdPutC(0x40, fp);
	} else {
		gdPutC(0x00, fp);
	}

	/* Write out the initial code size */
	gdPutC(InitCodeSize, fp);

	/* Go and actually compress the data */
	compress(InitCodeSize + 1, fp, im, &ctx);

	/* Write out a Zero-length packet (to end the series) */
	gdPutC(0, fp);

	/* Write the GIF file terminator */
	gdPutC(';', fp);
}

static void GIFAnimEncode(gdIOCtxPtr fp, int IWidth, int IHeight, int LeftOfs, int TopOfs, int GInterlace, int Transparent, int Delay, int Disposal, int BitsPerPixel, int *Red, int *Green, int *Blue, gdImagePtr im)
{
	int B;
	int ColorMapSize;
	int InitCodeSize;
	int i;
	GifCtx ctx;

	memset(&ctx, 0, sizeof(ctx));

	ctx.Interlace = GInterlace;
	ctx.in_count = 1;

	ColorMapSize = 1 << BitsPerPixel;

	if(LeftOfs < 0) {
		LeftOfs = 0;
	}
	if(TopOfs < 0) {
		TopOfs = 0;
	}
	if(Delay < 0) {
		Delay = 100;
	}
	if(Disposal < 0) {
		Disposal = 1;
	}

	ctx.Width = IWidth;
	ctx.Height = IHeight;

	/* Calculate number of bits we are expecting */
	ctx.CountDown = (long)ctx.Width * (long)ctx.Height;

	/* Indicate which pass we are on (if interlace) */
	ctx.Pass = 0;

	/* The initial code size */
	if(BitsPerPixel <= 1) {
		InitCodeSize = 2;
	} else {
		InitCodeSize = BitsPerPixel;
	}

	/* Set up the current x and y position */
	ctx.curx = ctx.cury = 0;

	/* Write out extension for image animation and looping */
	gdPutC('!', fp);
	gdPutC(0xf9, fp);
	gdPutC(4, fp);
	gdPutC((Transparent >= 0 ? 1 : 0) | (Disposal << 2), fp);
	gdPutC((unsigned char)(Delay & 255), fp);
	gdPutC((unsigned char)((Delay >> 8) & 255), fp);
	gdPutC((unsigned char) Transparent, fp);
	gdPutC(0, fp);

	/* Write an Image separator */
	gdPutC(',', fp);

	/* Write out the Image header */
	gifPutWord(LeftOfs, fp);
	gifPutWord(TopOfs, fp);
	gifPutWord(ctx.Width, fp);
	gifPutWord(ctx.Height, fp);

	/* Indicate that there is a local colour map */
	B = (Red && Green && Blue) ? 0x80 : 0;

	/* OR in the interlacing */
	B |= ctx.Interlace ? 0x40 : 0;

	/* OR in the Bits per Pixel */
	B |= (Red && Green && Blue) ? (BitsPerPixel - 1) : 0;

	/* Write it out */
	gdPutC(B, fp);

	/* Write out the Local Colour Map */
	if(Red && Green && Blue) {
		for(i = 0; i < ColorMapSize; ++i) {
			gdPutC(Red[i], fp);
			gdPutC(Green[i], fp);
			gdPutC(Blue[i], fp);
		}
	}

	/* Write out the initial code size */
	gdPutC(InitCodeSize, fp);

	/* Go and actually compress the data */
	compress(InitCodeSize + 1, fp, im, &ctx);

	/* Write out a Zero-length packet (to end the series) */
	gdPutC(0, fp);
}

/***************************************************************************
 *
 *  GIFCOMPR.C       - GIF Image compression routines
 *
 *  Lempel-Ziv compression based on 'compress'.  GIF modifications by
 *  David Rowley (mgardi@watdcsu.waterloo.edu)
 *
 ***************************************************************************/

/* General DEFINEs */

#define GIFBITS	12

#ifdef NO_UCHAR
typedef char char_type;
#else /* NO_UCHAR */
typedef unsigned char char_type;
#endif /* NO_UCHAR */

/*
 *
 * GIF Image compression - modified 'compress'
 *
 * Based on: compress.c - File compression ala IEEE Computer, June 1984.
 *
 * By Authors:  Spencer W. Thomas       (decvax!harpo!utah-cs!utah-gr!thomas)
 *              Jim McKie               (decvax!mcvax!jim)
 *              Steve Davies            (decvax!vax135!petsd!peora!srd)
 *              Ken Turkowski           (decvax!decwrl!turtlevax!ken)
 *              James A. Woods          (decvax!ihnp4!ames!jaw)
 *              Joe Orost               (decvax!vax135!petsd!joe)
 *
 */
#include <ctype.h>

#define ARGVAL() (*++(*argv) || (--argc && *++argv))

#ifdef COMPATIBLE /* But wrong! */
#	define MAXCODE(n_bits) ((code_int) 1 << (n_bits) - 1)
#else /* COMPATIBLE */
#	define MAXCODE(n_bits) (((code_int) 1 << (n_bits)) - 1)
#endif /* COMPATIBLE */

#define HashTabOf(i) ctx->htab[i]
#define CodeTabOf(i) ctx->codetab[i]


/*
 * To save much memory, we overlay the table used by compress() with those
 * used by decompress().  The tab_prefix table is the same size and type
 * as the codetab.  The tab_suffix table needs 2**GIFBITS characters.  We
 * get this from the beginning of htab.  The output stack uses the rest
 * of htab, and contains characters.  There is plenty of room for any
 * possible stack (stack used to be 8000 characters).
 */

#define tab_prefixof(i) CodeTabOf(i)
#define tab_suffixof(i) ((char_type*)(htab))[i]
#define de_stack ((char_type*)&tab_suffixof((code_int)1 << GIFBITS))

/*
 * compress stdin to stdout
 *
 * Algorithm:  use open addressing double hashing (no chaining) on the
 * prefix code / next character combination.  We do a variant of Knuth's
 * algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
 * secondary probe.  Here, the modular division first probe is gives way
 * to a faster exclusive-or manipulation.  Also do block compression with
 * an adaptive reset, whereby the code table is cleared when the compression
 * ratio decreases, but after the table fills.  The variable-length output
 * codes are re-sized at this point, and a special CLEAR code is generated
 * for the decompressor.  Late addition:  construct the table according to
 * file size for noticeable speed improvement on small files.  Please direct
 * questions about this implementation to ames!jaw.
 */

static void output(code_int code, GifCtx *ctx);

static void compress(int init_bits, gdIOCtxPtr outfile, gdImagePtr im, GifCtx *ctx)
{
	register long fcode;
	register code_int i;
	register int c;
	register code_int ent;
	register code_int disp;
	register code_int hsize_reg;
	register int hshift;

	/* Set up the globals:
	 *	g_init_bits - initial number of bits
	 *	g_outfile   - pointer to output file */
	ctx->g_init_bits = init_bits;
	ctx->g_outfile = outfile;

	/* Set up the necessary values */
	ctx->offset = 0;
	ctx->out_count = 0;
	ctx->clear_flg = 0;
	ctx->in_count = 1;
	ctx->maxcode = MAXCODE(ctx->n_bits = ctx->g_init_bits);

	ctx->ClearCode = (1 << (init_bits - 1));
	ctx->EOFCode = ctx->ClearCode + 1;
	ctx->free_ent = ctx->ClearCode + 2;

	char_init(ctx);

	ent = GIFNextPixel(im, ctx);

	hshift = 0;
	for(fcode = (long)hsize; fcode < 65536L; fcode *= 2L) {
		++hshift;
	}
	hshift = 8 - hshift; /* set hash code range bound */

	hsize_reg = hsize;
	cl_hash((count_int) hsize_reg, ctx); /* clear hash table */

	output((code_int)ctx->ClearCode, ctx);

#ifdef SIGNED_COMPARE_SLOW
	while((c = GIFNextPixel(im)) != (unsigned) EOF) {
#else /* SIGNED_COMPARE_SLOW */
	while((c = GIFNextPixel(im, ctx)) != EOF) {
#endif /* SIGNED_COMPARE_SLOW */

		++(ctx->in_count);

		fcode = (long) (((long) c << maxbits) + ent);
		i = (((code_int)c << hshift) ^ ent); /* xor hashing */

		if(HashTabOf(i) == fcode) {
			ent = CodeTabOf (i);
			continue;
		} else if ((long)HashTabOf (i) < 0) {/* empty slot */
			goto nomatch;
		}

		disp = hsize_reg - i; /* secondary hash (after G. Knott) */

		if(i == 0) {
			disp = 1;
		}

probe:
		if((i -= disp) < 0) {
			i += hsize_reg;
		}

		if(HashTabOf(i) == fcode) {
			ent = CodeTabOf (i);
			continue;
		}

		if((long)HashTabOf(i) > 0) {
			goto probe;
		}

nomatch:
		output((code_int) ent, ctx);
		++(ctx->out_count);
		ent = c;
#ifdef SIGNED_COMPARE_SLOW
		if((unsigned) ctx->free_ent < (unsigned) maxmaxcode) {
#else /*SIGNED_COMPARE_SLOW*/
		if (ctx->free_ent < maxmaxcode) {  /* } */
#endif /*SIGNED_COMPARE_SLOW*/
			CodeTabOf(i) = ctx->free_ent++; /* code -> hashtable */
			HashTabOf(i) = fcode;
		} else {
			cl_block(ctx);
		}
	}

	/* Put out the final code. */
	output((code_int)ent, ctx);
	++(ctx->out_count);
	output((code_int) ctx->EOFCode, ctx);
}

/*****************************************************************
 * TAG( output )
 *
 * Output the given code.
 * Inputs:
 *      code:   A n_bits-bit integer.  If == -1, then EOF.  This assumes
 *              that n_bits =< (long)wordsize - 1.
 * Outputs:
 *      Outputs code to the file.
 * Assumptions:
 *      Chars are 8 bits long.
 * Algorithm:
 *      Maintain a GIFBITS character long buffer (so that 8 codes will
 * fit in it exactly).  Use the VAX insv instruction to insert each
 * code in turn.  When the buffer fills up empty it and start over.
 */

static unsigned long masks[] = {
	0x0000, 0x0001, 0x0003, 0x0007, 0x000F,
	0x001F, 0x003F, 0x007F, 0x00FF,
	0x01FF, 0x03FF, 0x07FF, 0x0FFF,
	0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
};

static void output(code_int code, GifCtx *ctx)
{
	ctx->cur_accum &= masks[ctx->cur_bits];

	if(ctx->cur_bits > 0) {
		ctx->cur_accum |= ((long)code << ctx->cur_bits);
	} else {
		ctx->cur_accum = code;
	}

	ctx->cur_bits += ctx->n_bits;

	while(ctx->cur_bits >= 8) {
		char_out((unsigned int)(ctx->cur_accum & 0xff), ctx);
		ctx->cur_accum >>= 8;
		ctx->cur_bits -= 8;
	}

	/*
	 * If the next entry is going to be too big for the code size,
	 * then increase it, if possible.
	 */
	if(ctx->free_ent > ctx->maxcode || ctx->clear_flg) {
		if(ctx->clear_flg) {
			ctx->maxcode = MAXCODE (ctx->n_bits = ctx->g_init_bits);
			ctx->clear_flg = 0;
		} else {
			++(ctx->n_bits);
			if(ctx->n_bits == maxbits) {
				ctx->maxcode = maxmaxcode;
			} else {
				ctx->maxcode = MAXCODE(ctx->n_bits);
			}
		}
	}

	if(code == ctx->EOFCode) {
		/* At EOF, write the rest of the buffer. */
		while(ctx->cur_bits > 0) {
			char_out((unsigned int)(ctx->cur_accum & 0xff), ctx);
			ctx->cur_accum >>= 8;
			ctx->cur_bits -= 8;
		}

		flush_char(ctx);
	}
}

/*
 * Clear out the hash table
 */
static void cl_block (GifCtx *ctx) /* table clear for block compress */
{
	cl_hash((count_int) hsize, ctx);
	ctx->free_ent = ctx->ClearCode + 2;
	ctx->clear_flg = 1;

	output((code_int)ctx->ClearCode, ctx);
}

static void cl_hash(register count_int chsize, GifCtx *ctx) /* reset code table */
{
	register count_int *htab_p = ctx->htab+chsize;
	register long i;
	register long m1 = -1;

	i = chsize - 16;
	do { /* might use Sys V memset(3) here */
		*(htab_p - 16) = m1;
		*(htab_p - 15) = m1;
		*(htab_p - 14) = m1;
		*(htab_p - 13) = m1;
		*(htab_p - 12) = m1;
		*(htab_p - 11) = m1;
		*(htab_p - 10) = m1;
		*(htab_p - 9) = m1;
		*(htab_p - 8) = m1;
		*(htab_p - 7) = m1;
		*(htab_p - 6) = m1;
		*(htab_p - 5) = m1;
		*(htab_p - 4) = m1;
		*(htab_p - 3) = m1;
		*(htab_p - 2) = m1;
		*(htab_p - 1) = m1;
		htab_p -= 16;
	} while((i -= 16) >= 0);

	for(i += 16; i > 0; --i) {
		*--htab_p = m1;
	}
}

/******************************************************************************
 *
 * GIF Specific routines
 *
 ******************************************************************************/

/*
 * Set up the 'byte output' routine
 */
static void char_init(GifCtx *ctx)
{
	ctx->a_count = 0;
}

/*
 * Add a character to the end of the current packet, and if it is 254
 * characters, flush the packet to disk.
 */
static void char_out(int c, GifCtx *ctx)
{
	ctx->accum[ctx->a_count++] = c;
	if(ctx->a_count >= 254) {
		flush_char(ctx);
	}
}

/*
 * Flush the packet to disk, and reset the accumulator
 */
static void flush_char(GifCtx *ctx)
{
	if(ctx->a_count > 0) {
		gdPutC(ctx->a_count, ctx->g_outfile);
		gdPutBuf(ctx->accum, ctx->a_count, ctx->g_outfile);
		ctx->a_count = 0;
	}
}

static int gifPutWord(int w, gdIOCtx *out)
{
	/* Byte order is little-endian */
	gdPutC(w & 0xFF, out);
	gdPutC((w >> 8) & 0xFF, out);
	return 0;
}
